Benjamin was born in or near Paris, France, the son of the French publisher Nicholas Bonneville and his wife Marguerite Brazier.

The inheritance included 100 acres (40.5 ha) of his New Rochelle, New York farm where they had been living, so she could maintain and educate her sons.

While in Missouri, Bonneville was inspired by the writing of Hall J. Kelley, as well as editorials in the St. Louis Enquirer (edited at the time by Thomas Hart Benton) to join in the exploration of the American West.

Bonneville met with Kelley, who was impressed by him and appointed him to lead one of the expeditions to the Oregon Country; it was scheduled to leave in early 1832.

To pursue his desire to explore the west, he petitioned General Alexander Macomb for a leave of absence from the military, arguing that he would be able to perform valuable reconnaissance among the Native Americans in the Oregon Country, which at the time was under a precarious joint occupation of the U.S. and Britain.

Macomb granted his request, a 26-month leave running from August 1831 to October 1833, and instructed him to gather all information that might be useful to the government.

In particular, he was to pose as a fur trader and find out the natural history of the region, its climates, soils, geography, topography, mineral production, geology, and the character of the local tribes.

Expenses for his exploration were paid by private donors, including Astorian Alfred Seton and possibly John Jacob Astor.

[3] The expedition that would be known as the most notable accomplishment of his life began in May 1832, when Bonneville left Missouri with 110 men, with field lieutenants Michael Cerre and Joseph R.

It reached the Green River in August and built a fur trading post,[2] which it named Fort Bonneville.

[4] He also sent a party of men under Walker to explore the Great Salt Lake and find an overland route to California.

Some historians have speculated that he was attempting to lay the groundwork for an eventual invasion of California, then part of Mexico, by the United States Army.

He wrote a lengthy letter to General Macomb summarizing some of his findings and requesting more time, specifically to survey the Columbia River and parts of the Southwest before his return.

After spending the early winter at Fort Bonneville, he set out westward in January 1834 with the goal of reaching the Willamette Valley.

Empty handed, Bonneville and men retraced their course back to southeast Idaho and made camp on the Portneuf River.

He spent the winter of 1834–35 with the Shoshone along the upper Bear River, and in April 1835 began the voyage back to Missouri.

The two of them agreed that for the sum of $1000 ($27,745 in 2023 dollars [5]), Bonneville would turn over his maps and notes so that Irving could use them as the basis for his third "Western" book.